Uplink Massive MIMO Functional Split for C-RAN System Under Rapid User Mobility Conditions

Abstract

Uplink massive multiple-input multiple-output (MIMO) improves network spectral efficiency by enabling simultaneous transmission from multiple users through spatial multiplexing. Although the centralized radio access network (C-RAN) architecture can meet the increased signal processing requirements, the large number of used antenna elements creates challenges for the fronthaul (FH) links required to transport a large amount of traffic from remote radio units (RRUs) to the centralized baseband unit (BBU). To reduce the FH link load, different baseband splitting options between RRUs and BBU are considered in practical C-RAN networks. More specifically, low complexity maximum ratio combining (MRC) beamforming at the RRU can be used to reduce the number of spatial dimensions of the received signals before transporting them to the BBU for further baseband processing. Despite the high compression efficiency of the MRC-based approach, we find that its performance is not sufficiently robust under channel varying conditions due to rapid user mobility. In this paper, we propose a functional split based on an extension of MRC compression at the RRU which provides better uplink performance for scenarios with high mobility, while guaranteeing moderate FH link throughput and low signal processing complexity.